Cancer Constellation, the Astronomer’s Guide to the Crab in the Sky

Star constellations are where astronomy meets astrology, as the images that the constellations form are linked to many stories and myths. The Cancer constellation is not only a group of stars but also one of the twelve horoscope signs, making it a fascinating part of the night sky!  

It supposedly represents a crab, which is hard to see considering the constellation is quite faint and is merely a few stars in a Y shape. But that’s where a little imagination can go a long way! 

The Constellation of Cancer

The constellation of Cancer is one of the twelve zodiac signs, and its name means ‘crab’ in Latin. That is why it is represented as a crab, despite it being hard to picture one when you look at it in the night sky.

It’s a medium-sized constellation, covering 506 square degrees of the sky. This makes it the 31st largest constellation out of the 88 that are recognized in star maps!

However, despite being quite big, it’s not a very bright constellation, with most of its stars being rather faint. That is why it can be very hard to spot, but if you do, you will recognize it as a faint upside-down Y. 

The constellation has 10 named stars in total, some brighter than others. As one of the twelve zodiac signs, it has plenty of myths and stories to go with it, but other than that, it doesn’t really account for much more.

Nevertheless, let’s look at some of the most interesting facts about the Cancer constellation: 

  • In Greek mythology, it is said that while Hercules was fighting the Hydra monster, Hera sent a crab to thwart him and make him lose. However, Hercules won against the Hydra, and he killed the crab. Hera then placed the crab amongst the stars, and it became a constellation. 
  • As the Cancer constellation is one of the faintest, with its brightest star having only a 4th magnitude, it has often been referred to as the “Dark Sign” of the sky, or as a black crab with no eyes. 
  • The Tropic of Cancer is a line of latitude that goes around the Earth, and it is the most northerly point where the sun can be directly overhead during the June Solstice. The reason it is named after Cancer is that it was named 2000 years ago when the sun so happened to be in the Cancer constellation during the summer solstice. 
  • The constellation of Cancer is one of the twelve zodiac sign star constellations, belonging to those born between June 21st and July 22nd. It’s a water sign, and it is often associated with the moon, emotions, and kindness. 
  • When written down as a symbol, cancer is often depicted with the number 69 lying on its side, as it supposedly represents the crab’s claws. 

How to find Cancer in the night sky

The constellation of Cancer is one of the dimmest in the sky, as none of its stars are especially bright. That is why it can be quite tricky to find if you don’t know exactly where to look.

It is located in the Northern celestial hemisphere, and its closes neighbors are the Gemini constellation to the West, Lynx to the North, Leo Minor to the Northeast, Leo to the East, Hydra to the South, and the Canis Minor constellation to the Southwest. 

To find it, using the constellations that border it, you can draw an imaginary line between Regulus in the Leo constellation, all the way to Pollux in Gemini. At the midpoint of this line is where the middle of Cancer should be located! 

If you’re trying to find the constellation from the Northern hemisphere, it can best be seen in early spring evenings. Meanwhile, if you’re trying to find it from the Southern Hemisphere, it can best be seen during autumn. 

It first appears over the horizon in December, rising towards the zenith in March and then sinking back down towards June. It’s also important to remember that it isn’t visible during the evenings between July and November if you’re in the Northern hemisphere. 

As we’ve said, it can be quite hard to find the Cancer constellation, so don’t get frustrated if you don’t manage to find it on your first try! Having a map of the stars in your area or using an automated telescope can really help if you keep on struggling!

The brightest stars in the constellation of Cancer

The Cancer constellation has a total of 10 named stars, only two of which are bright enough to be above a fourth magnitude, which explains why it’s so dim and hard to spot in the night sky. 

Let’s take a look at the ones that stand out the most within the constellation: 

Acubens:

Also known as the Alpha Cancri, this star has a magnitude of 4.25.

The reason why it’s one of the brightest stars in the Cancer constellation is that it is actually a quadruple star system of four, which is approximately 174 light-years away. 

Tarf:

Also known as the Beta Cancri, this star has a magnitude of 3.5. It’s a binary star system, and it is actually the brightest star within the Cancer constellation.

The primary star is an orange giant, with its companion being a magnitude 12. It is located approximately 290 light-years away! 

Asellus Australis:

Also known as the Delta Cancri, this star has a magnitude of 3.94, with it being an orange giant. It’s the second brightest star in the Cancer constellation and is located approximately 180 year-lights away.

It is also sometimes referred to as the Beehive cluster, as that is where it’s located! Oh and fun fact, Asellus Australis means “Southern donkey colt” in Latin! 

Asellus Borealis:

Also known as the Gamma Cancri, this star has a magnitude of 4.66 and is a white subgiant. Located around 158 year-lights away, it can often be hidden by different planets and even by the moon, so it’s not one of the brightest.

Fun fact, it translates from Latin as the “Northern donkey colt”! 

Copernicus:

Also known as the 55 Cancri, this is a double star with a yellow dwarf and a red star of magnitude 16.

This pair of stars is one of the closest, at only approximately 41 light-years away! 

Tegmine:

Also known as the Zeta Cancri, this is another cluster of stars, with the main one having a magnitude of 4.67.

It is located approximately 83 light-years away, also making it one of the closest to us! 

Decapoda: 

Also known as the Lambda Cancri, this star has a magnitude of 5.92 and is located approximately 419 light-years away.

It’s a blue-white dwarf, a lot hotter and bigger than our own sun. 

Nahn:

Also known as the Xi Cancri, this is a double star with a magnitude of 5.16. It is located approximately 381 light-years away, As it is a spectroscopic binary star, we can only tell that it has a partner thanks to the periodic dimming and brightening of the main one. 

None of the stars from the Cancer constellation are of any special interest, other than them being a part of the constellation itself. That is why, when observers are looking for the Cancer constellation, it is often so that they can observe the Beehive Cluster.

It’s right in the middle of the constellation, located in the same place as the Ausellus Australis star. 

This cluster of stars is located approximately 590 light-years away, and it is one of the nearest to our Solar System, making it one of the best to observe, especially when the Cancer constellation is high up in the sky. 

The Beehive Cluster is sometimes described as the nebulous mass in the breast of Cancer, and it actually one of the first sky objects that Galileo himself observed through a telescope in 1609!

Conclusion

The Cancer constellation, being one of the twelve zodiac signs, is known as the crab. It’s a medium-sized constellation situated in the Northern celestial hemisphere.

Despite its size, it’s not very easy to spot, as the stars that make it up aren’t very bright. It has 10 named stars, with eight that are decently bright enough to mention. It is also home to the Beehive Cluster of stars, which is one of the closest to our Solar System! 

It has plenty of myths and stories to go with it, thanks to it being a zodiac sign, and in Greek Mythology, it represents the crab that Hera sent to bite Hercules while he was fighting the Hydra monster. 

As it’s hard to spot in the night sky, you can use the brighter neighboring constellations, such as Leo and Gemini, as a reference to find it!

Andy Morgan